In the 1980 presidential election, Ronald Reagan won decisively against incumbent Jimmy Carter. The popular vote of 51% to 41% translated into a 44 state, 449 electoral college landslide. Republicans made gains in the US House of Representatives and elected 12 new senators, finally giving the GOP control of one house of Congress. A new day had dawned.

Or had it? The coalition that put Reagan in the White House turned out to be less conservative, and less radical, than the would-be reformer. In fact, Reagan found it impossible to hold it together over his eight-year presidency. In 1986, most of the freshmen senators who won in 1980 went down to defeat. The Republicans wouldn't retake the Senate until President Bill Clinton made a hash of things in 1994.

Early on, Reagan found his proposals bottled up in Congress. Stephen Slivinski, author of a book on fiscal history of the Republican party called Buck Wild, points out that most of Reagan's spending proposals were a dead letter on Capitol Hill right up until the president was shot by mad gunman John Hinckley. "What the assassination attempt did was give Reagan a second political honeymoon," Slivinski told me.

Why mention Reagan now? Because the new president-elect, Barack Obama, has taken some heat in the past for praising his presidency. Obama understands that Reagan benefited from history. He came along at the right moment to attract a critical mass of voters who were ready for change, even if they didn't sign onto all the particulars of Reagan's agenda.

Obama is drawn to the felicity of the Reagan presidency, as opposed to the grimness of George Bush's recent tenure. That's good, as far is it goes, but I'm not sure he understands the possible downside of emulating Reagan.

Bush divided and conquered. With the help of political Machiavel Karl Rove, Bush assembled two narrow coalitions around deep cultural divisions, and then didn't feel particularly constrained by those coalitions.

Economic conservatives got tax cuts set to expire at the end of Bush's time in office. Evangelicals got limited funding for faith-based charities and a veto on funding embryonic stem cell research, but very little else.

During the campaign, Obama reached out far beyond the usual Democratic interest groups. In fact, during the presidential debates, it was Obama, more often than Senator John McCain, who sounded like a Republican. He promised fiscal prudence and middle class tax cuts and real respect for his political opponents.

That helped Obama win states most Democrats couldn't. At press time, he had racked up 349 electoral college votes to McCain's 147. But many of those states were won narrowly and will not be an easy hold in four years, and so now Obama has to make a choice. A President Obama who wants to win next time in Virginia, say, will have to behave very differently than a President Obama who is happy to win all of the usual Democratic states plus Ohio or Florida.

Unless he is willing to shed parts of the coalition that put him in the White House, Obama could very well end up a victim of his own success.